1. Field of the Invention
This invention relates to electronic measuring apparatus. More specifically, this invention relates to a stand-alone electronic measuring apparatus for utility AC power systems incorporating analog voltage and current inputs, digital inputs, trigger event processing, and coupling to telephonic facsimile apparatus without an intervening computer system.
2. Background of the Invention
It is often necessary to read the results of an instrument on a utility power distribution system at some distance from where it is located. For example, the power flow through a particular transformer may be read by an operator at an office miles away, or the power factor of a branch circuit leaving a substation may be checked electronically without physically visiting the substation. Early remote instruments were connected to their output devices by direct cables. More recent instruments may employ communication techniques such as power line carrier, radio transmission, or the telephone switching network to transmit their readings.
If an instrument is read frequently enough, it may be appropriate to install a remote output device that is dedicated to the instrument. But if the information from the instrument is required infrequently, it is common practice to employ an output device, typically a computer, that can be shared between several instruments. For example, a single personal computer can easily be employed to occasionally interrogate and report on the status of several power quality instruments on a single power distribution network. This approach works well with many kinds of measurements.
However, if the instruments are a trigger-type instruments (that is, they are instruments that need to report their data at unpredictable intervals) with limited ability to store the measurements, a remote output device, typically a personal computer, must be standing by at all times to receive the measurements, or data may be lost. For example, if the instrument is an AC power system lightning strike recorder with sufficient storage space for data about a single lightning strike, and it records a strike, it must either be able to communicate its measurements to its remote output device before it detects a second lightning strike or lose its data about subsequent lightning strikes.
At utility companies, it is often difficult to economically justify dedicating a personal computer to standby communications from instruments, especially if the communication are infrequent. Even when a personal computer can be justified, it is often difficult to economically justify the associated outside telephone line required for that computer.
In some systems, such as the one disclosed by French et al. in U.S. Pat. No. 5,061,916, the output of remote instruments in a building automation system are coupled to a central control computer which in turn generates and transmits a report to a standard facsimile apparatus. This approach succeeds in remotely presenting the data collected by the instruments, but does not succeed in eliminating the requirement to dedicate a personal computer and its associated communication network to standby communications from instruments.
When making remote AC power system measurements, it is often necessary to check the measured data at an arbitrary time. For example, a utility company may receive an urgent telephone call from a customer requesting information about power line disturbances that have taken place in the last fifteen minutes. In situations like this, the user of a remote AC power measurement system may need to request that the remote sensor provide a report immediately, whether or not any triggering event has occurred.
The French reference does not disclose any method for instructing their building automation system to generate a report in response to a request signal.
The present invention solves the problem of requiring a standby computer by coupling the output of a remote AC power instrument directly to a facsimile apparatus via the telephone system without an intervening computer.
The present invention solves the problem of generating a report in response to a request signal by instructing the remote instrument to generate and transmit a report whenever it receives a phone communication that it cannot otherwise process, thus allowing a user to trigger a report by simply telephoning the instrument, waiting for it to answer, then hanging up.